The present invention relates to a millimeter wave radar mounted on a vehicle.
A millimeter wave radar is used for the purpose of automatic operation or collision prevention of a vehicle. The millimeter wave radar is a system for transmitting a millimeter electromagnetic wave in a desired direction, receiving the reflection of the transmitted wave, and preliminarily detecting a body which may act as an obstacle. On the other hand, the millimeter wave radar has the problem that the side lobe of the transmitted electromagnetic wave is reflected by surrounding bodies, with the result that unnecessary bodies would also be detected. As a countermeasure against this problem, a technique of mounting a metallic plate or an absorber to the periphery of the transmission-reception antenna surface in the antenna unit in the state of projecting from the surface of the transmission-reception antenna so as thereby to reduce the side lob has been described, for example, in Japanese Patent Laid-open No. 10-126146.
However, according to the technique described in Japanese Patent Laid-open No. 10-126146, since the metallic plate or absorber mounted to the periphery of the transmission-reception antenna is separate from the radome, the structure and production process of the antenna unit become complicated. In addition, the metallic plate or absorber itself must have a certain degree of strength, so that the metallic plate or absorber itself must be thick to a certain extent, resulting in the problem of an increase in weight. Furthermore, since the metallic plate or absorber is exposed to rain and winds, it has still the problem in weathering performance.